Xantia V6 4HP20 driving modes not working?

[DSFan]

Hello all fellow Citroenists!

I just registered here to ask about behaviour of my 97 Xantia V6 4HP20 transmission.

Problem is that either Snow or Sport mode buttons dont light up and the modes dont activate either.
They worked well before, about couple of weeks ago but one day they just didnt anymore.
Just when i was going to demonstrate the exellence of theV6 Xantia

The transmission works just fine, like it supposed to.
Kickdown works, all stick positions work and today i had the oils checked at the shop. They were ok by them.

So i reckon the problem is in electrics somewhere. Could someone please give some advise or educated quess what could be wrong?
I could not find bad fuse, perhaps relay, wiring harness, connector..?

Thank you in advance!!

Cheers

Mike

[CitroJim]

Welcome to the forum Mike

Sounds like the wiring between the buttons and the ECU has failed or the panel itself. It does have electronics on it. They're not simple switches. they operate electronic latches on the panel.

I'd be temped to have a Lexia diagnostic run first and then it'll be sitting down with the diagrams, which I can supply, and work out what's gone wrong...

Where are you located?

[Mandrake]

Welcome Mike,

Interesting problem - I haven't seen it reported before, but its probably not a major fault.

A Lexia test might be helpful including the "parameters measurement" section which can show live input data from the controls including gear lever and sport/snow buttons, but I suspect that all it will show is what we already know - that the ECU isn't receiving any signal from those buttons, but it won't tell us the reason why.

You may find the following document for the 4HP20 very helpful, it's basically the bible for understanding the workings of the gearbox both mechanical and electrical:

https://dl.dropboxusercontent.com/u/782 ... aining.pdf" onclick="window.open(this.href);return false;

If you check page 109 (header page numbering not PDF page number) you'll see the wiring diagram for the sport/snow control assembly for a S1 Xantia, while page 110 has the wiring for a S2 Xantia, which is different. I'm assuming from 1997 that yours is a Series 1 like mine with the lights beside the buttons...

In which case, with a multimeter I would check the power on pins 1 and 4 first (and ground on pin 6) and then the outputs to the ECU on pins 7 and 2 in response to pressing the buttons.

If the lights also don't work its most likely either a power/ground issue or a fault on the module itself - whilst a fault in the two wires to the ECU would prevent the ECU switching to sport/snow, I don't think it would prevent the lights from indicating the desired mode...

[DSFan]

Hi, and thank you for answer!

My friend has a Lexia and propably, at suitable time, i will dive in.
The techsheet of the box that Simon linked is welcome and i will first try to find if some connector or earth issue can be found.
I appreciate the offer from Jim for help but i do live in Finland, so distance is an issue

I was allso looking for threads about sparkplugs and found one too.
I had mine replaced but there seems to be difficulties to start sometimes when engine is warm. I have to start about 3 times and idle is then little wobbly. It helps a little if i put aircon off for the time of starting the thing...
Unfortunately i have no info about the spark the garage put in, suppose they just followed some instructions about them...

I just Love my V6. I have had her for just a couple of months and am still getting to know the beast. It is quite different from BX GTI (1.6) i had before!!

[CitroJim]

Yes, Finland is quite a trek from my place

V6 warm starts are not smooth. The wobbly idle after a warm start is perfectly normal and sometimes it is so bad the engine can stall. So long as the engine readily fires up when cold then no worries! I just wait it out until the idle settles.

The spark plugs in the rear bank require the inlet manifold to be removed and some people don't bother with hose and just replace the spark plugs in the front bank. If they do replace the rear bank ones they may not renew the inlet manifold gasket. The gasket is very cheap from a dealer so there's no excuse but often the old gasket is not good to reuse and it can cause air leaks. That can affect the quality of warm starts.

[Mandrake]

I'd say difficult hot starts followed by a wobbly idle for 5-10 seconds are quite common on this engine although not necessarily "normal". (Did they do it when new I wonder ?)

From my experimentation I think there are a couple of contributing factors to this as my previous V6 suffered from this really badly for a while - to the point where a hot start would be followed by a complete stall on the first couple of attempts to start...

I think the biggest factor is fuel rail bleed down causing vapour lock in the fuel rail. When the engine is turned off the fuel rail should hold a steady pressure for at least 15 minutes with no more than about 10% drop in pressure - typically after turn off the initial pressure will be around 2.3 bars, so it should stay above about 2 bars for at least 15 minutes.

The pump is also periodically energised for about a second to "top up" the fuel rail pressure when the engine is off to minimise the chance of vapour lock. I'm not sure exactly how often but it's something like once every 5 minutes for about 20 minutes the pump will come on for just a second then go off - even if you've locked and left the car. (Beware of this happening if you're changing a fuel filter and forgot to disconnect the battery!)

On a hot engine if the fuel pressure drops quickly after switch off the fuel in the rail will immediately boil and will stay in a vapour state for a long time (at least half an hour) and during that time it will be very hard to start with an unstable wobbly idle until the vapour is circulated back to the tank and replaced with fresh cold fuel.

To see if this is happening, connect a fuel pressure gauge to the schrader valve on the end of the front fuel rail - you'll need to remove the air filter box and one of the bolts for the cruise control vacuum diaphragm to tilt it out of the way a bit.

After running the engine for a minute turn it off and watch the fuel pressure reading - on a good system it should immediately drop slightly and then stay more or less constant above 2 bars for at least 10-15 minutes. If the pressure completely bleeds away in 1-2 minutes or less then there is a bleed down problem that will be contributing to difficult hot starting...

If there is a bleed down problem the next step is to find the source of the leak - it can be either the non return valve in the in-tank pump (most common) an internal leak in the pressure regulator (less common) or a leaking injector. A leaking injector is very unlikely however if one is leaking it will make starting very difficult as one cylinder will be flooded when you first try to start. (This would tend to cause trouble with cold starts too though)

Run the engine, switch it off, and then use a pair of pliers to carefully pinch off the supply fuel line connected to the rear fuel rail - between the rail and where it goes over the top of the cam belt cover...If the pressure holds instead of dropping you know its the in-tank pump at fault. If not try the test again and pinch the return (front) hose from the regulator, if that stops the drop it's a leaky regulator. If you pinch both off at the same time and it still keeps dropping its a leaky injector.

On my old V6 the source of the leak was the in-tank pump, and the leak down was somewhat intermittent - sometimes it would leak quickly, sometimes very slowly, probably due to wear in the non-return valve. I ended up replacing the fuel pump in that car with a £65 Bosch one (from mr-auto I think) and the bleed down problem went away. It didn't eliminate the wobbly idle on a hot start entirely but made it much less severe and it no longer stalled outright.

Another factor that I think can contribute to this wobbly near-stall and recover behaviour after a hot start is a sticky or badly worn ICV (idle control valve) which prevents the ECU from making accurate corrections to the idle speed - when the speed is a bit low it tries to open the valve a bit, the valve doesn't actually move because its ever so slightly stuck so it keeps increasing the signal to the ICV until it suddenly "jumps" causing the idle speed to shoot up too high, then the same thing happens in reverse, so you get a series of over corrections until it settles down.

This can also happen when you pull to a stop at traffic lights in gear and the idle speed drops too slow and then surges too high - for the same reason that the ICV is not moving smoothly.

On my new V6 the ICV (after cleaning it) is in a lot better condition than the old V6 and it doesn't suffer from this wild fluctation in idle speed on a hot start - it can still be a little bit unstable after a hot start so I suspect that it too has a worn non return valve in the fuel pump. I'll be checking the fuel rail pressure and bleed down on the new V6 soon - the pump is very noisy and I suspect may be in need of replacing... fortunately the £65 after market Bosch pump seems pretty decent when an OEM type is nearly £200!

[CitroJim]

I'd say difficult hot starts followed by a wobbly idle for 5-10 seconds are quite common on this engine although not necessarily "normal". (Did they do it when new I wonder ?)

I don't know Simon but all the V6s I've owned have done it to a lesser or greater extent. That's four and counting

[Mandrake]

I'd say difficult hot starts followed by a wobbly idle for 5-10 seconds are quite common on this engine although not necessarily "normal". (Did they do it when new I wonder ?)

I don't know Simon but all the V6s I've owned have done it to a lesser or greater extent. That's four and counting

I'd still call it a common fault rather than an inherent characteristic...

My new V6 almost doesn't do it at all. Only if the engine bay is very very hot on a hot day. Then it will fluctuate a little bit for a few seconds on a hot start, but nothing like the old V6 did where it was almost stalling and recovering.

On a warm start when the engine is warmed up but the engine bay is not yet thoroughly heat soaked it starts perfectly and there is almost no waver in idle speed after starting.

I think leaky non-return valves in the in-tank pumps is just a very common problem when they get older, and the only symptom is a bleed down issue - it won't cause problems after the engine is running. Both the original fuel pump in the old V6 AND the second hand fuel pump I got from KP and fitted to the car for a while had the same issue of rapid pressure bleed down. Only after I fitted the new Bosch pump did the bleed down issue stop.

Try a bleed down test on yours Jim, see if it has the issue or not. Unless the pump has been replaced I'll bet you anything that it loses rail pressure quickly.

[CitroJim]

Simon. I'll do that test. It's the ideal time with it still in bits having the cambelt and pump done.

It won't be yet as I'm out of action due to a crushed finger. I'll just be a keyboard mechanic for a while

I reckon it's a close call whether or not it's a characteristic or a very common fault

[DSFan]

Simon, the bleed-down issue at the pump sounds quite like mine V6:s symptoms. It does this every time when warm weather and/or hot engine, but lot less when it is chilly. Cold start is allways perfect. Hot restart often ends up with a stall after short wobbly idle.
Usually 3´rd attempt starts it ok...
It is really not that annoying but I´ll have to take a look at this at some point. Thanks.

Something interesting happened today tough. I started the engine to raise the car up, to spray some anticorrosion spray at the back wheel section, and by a chance i decided to try the S/Snow buttons. Surprise war great since the Sport mode button lit up! Weird.
I then depressed it and decided to make same to the snow button but that did´t light up... Odd...
Gear was in P and i allso put it on D and N when pressing the snow but it did not react at all...

I allso have noticed that sometimes after warm start, the window gets all steamed.
Goes away rapidly after i switch on AC. I am afraid it is the heater... :/

Some mysterious spirit lives in the car, or my Xantia is just getting bit old
Seriousely speaking, i am aware many of the usual faults these things suffer.
Just hope that ALL of them would not bother me (at least not at the same time)...

[CitroJim]

I allso have noticed that sometimes after warm start, the window gets all steamed.
Goes away rapidly after i switch on AC. I am afraid it is the heater... :/

Sounds like the heater matrix is leaking a little. A very common fault on a Xantia

Can you smell curry in the car when the heater is on? It's a sure sign if you can.

The job to replace the heater matrix is not technically hard, just long and tedious as the whole dash needs to be removed.

Some mysterious spirit lives in the car, or my Xantia is just getting bit old

No, yours is not unusual, that mysterious spirit lives in all Xantias and causes much mischief

[addo]

ES9s here have quite a stable idle at cold start; the fluctuation may be a cold temperature issue.

[CitroJim]

ES9s here have quite a stable idle at cold start; the fluctuation may be a cold temperature issue.

Cold starts are never the problem Adam, it's warm starts that can see the idle all over the place initially...

[Mandrake]

Simon. I'll do that test. It's the ideal time with it still in bits having the cambelt and pump done.

It won't be yet as I'm out of action due to a crushed finger. I'll just be a keyboard mechanic for a while

I reckon it's a close call whether or not it's a characteristic or a very common fault

How does this compare to your V6 Jim ?

I recorded this after the car had been parked for about 15 minutes following a 30 minute drive that had the engine bay nice and hot and the engine up to operating temperature:

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Just one slight dip in RPM, otherwise perfectly steady and smooth. Most hot starts on new V6 are like this. So it is possible!

I tried to do a pressure bleed down test as I also wanted to check the fuel pressure on new V6 for other reasons but unfortunately my fuel pressure gauge has decided to leak like a sieve. Not only is the purge port flowing all the time as if I had the button pressed down, fuel is even leaking out past the button. So I guess the purge button seals in the gauge have failed...

[CitroJim]

That's very impressive for a warm start Simon

Sorry to hear your gauge has died. It's come out in sympathy with your old car....